Reduction roasting of ore



May 15, 1957 L. G. HENDRICKSON 3,320,049

REDUCTION ROASTING OF ORE 2 Sheets-Sheet l Wafer Chamber NVENTOR. LUTHER 6. HENDCKSON B l y rf/I A t forney May 16, 1967 L. G. HENDRICKSON 3,320,049

REDUCTION ROSTING OF ORE Filed April 27, 1964 2 Sheets-Sheet 2 A Water Fan I f- 32 Fan I I, Fa 27\ l,.. Q Waste Gases l ,r 28

,l *Vent t`o `Y" cyclone Atmosphere 29 I Ir `Sc'rubtzer I I l I l I Combustion 30 i I 3/ 4 Chamber 4 z I Kiln Dry/'ng I I y l 1 I .1 I I Cyclone g l Damp Ore 22 26 l I Reduced Dust I Dry 0re I to Product I y I Kiln Heating (25 i and Reduction Air I I Fuel I l I Combustion I 23 I Chamber t 4 Kiln Cao/ing I l and Reduction l ya v y Unreduced Dust-l 24 J Reduced Ore ta Product N VEN TOR. L U THE R G. HENDR/CKSON Attorney United States Patent O 3,320,049 REDUCTION ROASTING F ORE Luther G. Hendrickson, Duluth, Minn., assigner to United States Steel Corporation, a corporation of Delaware Filed Apr. 27, 1964, Ser. No. 363,005 15 Claims. (Cl. 7S-1) This invention relates to improved methods and apparatus for reducing hematite to magnetite.

Most hematite (Fe203) found in nature is substantially nonmagnetic. One method of lbeneiiciating low grade hematite ore involves converting the hematite to magnetite (Fe304), which is magnetic, and separating the magnetite from the gangue material by magnetic means. Hematite can be converted to magnetite by a reductionroasting process, in which a reducing agent acts on the ore at an elevated temperature. Previous reductionroasting processes have had disadvantages, such as offering poor heat economy or low unit capacity, or they require careful preparation of the ore or reductant.

An object of my invention is to provide improved reduction-roasting methods and apparatus which largely overcome (the foregoing disadvantages.

A further object is to provide reduction-roasting methods and apparatus which have improved means for handling and recovering dust from the ore.

A further object is to provide reduction-roasting methods and apparatus which require fewer elaborate seals in the equipment and which utilize low-cost reducing agents, for example gas obtained from incomplete combustion of coal, although other reducing gases, such as producer gas or reformed hydrocarbons of course can be used.

In the drawings:

FIGURE 1 is a schematic owsheet of one arrangement of reduction-roasting apparatus in .accordance with my invention;

FIGURE 2 is a schematic owsheet of a modified arrangement; and

FIGURE 3 is a schematic owsheet of another modified arrangement.

The apparatus shown in FIGURE l includes three rotary kilns 10, 12 and 13, through which hematite ore fines pass continuously and in succession. Each kiln has a simple gas seal at each end, and the ore travels between kilns through suitable gas-tight ducts of known construction (not shown). In kiln I dry and preheat the ore to a temperature of about 1000 to 1500 F. In kiln 12 I reduce hematite in the ore to magnetite, which leaves the kiln at a temperature of about 1100 to 1800 F. In kiln |13 I cool the ore to a suitable handling temperature of about 300 to 600 F.

Strong reducing gas for reducing the ore continuously enters kiln 12 at a temperature of about 1800 to 2400 F. and leaves at a temperature of about 1200 to 1900 F. The gas flows through this kiln in the same direction as the ore. I illustrate the strong reducing gas as generated in a combustion chamber 14, to which I introduce fuel (for example coal) and sufficient air only for incomplete combustion of the fuel. Reducing gas formed in this manner typically has a composition on a dry basis about as follows:

Nevertheless it is apparent I can form the reducing gas in other ways, and that its composition may vary from this example.

Hereinafter I describe the origin of gas used in kiln 13. Gases from yboth kilns 12 and 13 go continuously to a settling chamber 15, where dust settles out. Hematite in this dust has been reduced to magnetite. I quench this dust in water and add it to the final product. In the example the two gases going to the settling chamber typically have compositions on a dry basis about as follows:

Kiln 12 gas, percent Kiln 13 gas, percent 12 1. 5 3 0. 5 12 18 72 79 2 5 0. 5 Hydrocarbon 0. 5 0. 5

The combined gases from the settling chamber ,go continuously to kiln 10. They are -at a temperature of about 1200 to 1700 F. as they enter the kiln, and they flow through the kiln in a direction counter to the ore. I also continuously introduce combustion air to this kiln. Sensible heat in the gases and heat produced by their combustion furnish the heat needed to dry and preheat the ore. The gases leave kiln 10 at a temperature of about 300 to 500 F., and their composition on a dry basis is similar to the composition of the gas leaving kiln 13.

Gas from kiln 10 goes continuously to a cyclone 16, where unreduced dust is removed. This dust goes to kiln 12, where the hematite therein is reduced to magnetite along with ore from kiln 10. From the cyclone the gas goes to a water scrubber 17. A fan 1S then forces gas continuously from the scrubber into kiln 13. This gas flows through the kiln in a direction counter to the ore and serves to cool the ore. The ,gas is mildly reducing and hence also serves to prevent reoxidation of the magnetite before it cools to a suitable handling temperature. The gas of course is heated as it cools the ore. I provide a damper-controlled bleed-off 19 between fan 18 and kiln 13 to remove a quantity of weak reducing gas sufiicient to balance the input of strong reducing gas to the system.

FIGURE 2 shows a modification in which unreduced ydust from cyclone 16 goes to a fluidized bed reactor 20 instead of joining the ore in kiln 12. I reduce the dust in the reactor by blowing into the hed fuel and air sufficient for partial combustion, as known in the art. I replace the settling chamber of FIGURE 1 with another cyclone 21. Dust-laden gas from reactor 20 passes through cyclone 21, from which the gas .goes to kiln 10 and the recovered dust is quenched and joins the final product. Gases from kilns 12 and 13 go directly to kiln 10 without an intermediate dust-removal step. In other respects this modification is similar to the embodiment shown in FIGURE 1.

FIGURE 3 shows another modification in which the ore passes successively and continuously through three kilns 22, 23 and 24. Kiln 22 is simply a countercurrent drying kiln, where I -heat the ore only moderately, for example to about 300 F. This kiln requires no gas-tight seal, while the other kilns have simple gas-tight seals asin the embodiments already described. I provide a gastight duct (not shown) between kilns 23 and 24 to conduct solids and gases in opposite directions. I reduce hematite in the ore to magnetite, which leaves the kiln at a temperature of about 1100 to 1800 F. In kiln 24 I cool the ore to a suitable handling temperature of about 300 to 600 F.

Reductant for reducing the ore continuously enters kiln 23 from a first combustion chamber 25 and flows counter to the ore. The reductant is a mixture of CO and H2, preferably formed by incomplete combustion of propane at a high temperature (for example 2400 F.) Nevertheless I can use other means for supplying gaseous re- In kiln 23 ductant, for example a coal gas producer (1200 F.) or a catalytic autothermal gas reformer (1600 F.). Since these alternatives produce gas at low temperatures, it may be necessary to burn part of the gas to supply sufficient heat, either in the kiln or in another chamber (-not shown). The reductant is diluted with other gas, as hereinafter explained, and enters kiln 23 at a temperature of about 1500 to 1600 F.

Gas leaves kiln 23 at a temperature of about 300 to 600 F. and goes to a cyclone 26, Where dust settles out. Hematite in the dust has been reduced to magnetite. I quench this dust and add it to the final product. Gas from the cyclone is combustible and reducing. A portion of this gas goes to a Water scrubber 27, from which a fan 28 continuously `directs it to kiln 24. The gas enters the kiln at a low temperature (for example about 100 F.) and passes through the kiln counter to the ore to cool the ore and protect it against reoxidation. The gas of course is heated in the kiln, and returns to kiln 23 Where it supplements the reductant from chamber 25, carrying along dust. A second fan 29 continuously directs the remainder of the .gas from cyclone 26 to a second combustion charnber 30, where the gas burns in air to raise its temperature to about 1800 to 2000 F. The products of combustion go continuously to kiln 22 `and thence to a cyclone 31. Unreduced dust recovered in the cyclone goes to kiln 24 from which the gas stream carries it back to the second kiln 23, where it is reduced. A third fan 32 directs waste gas from cyclone 31 to the atmosphere.

F rom the foregoing description it is seen that my invention affords a simple process and apparatus for reductionroasting of hematite to magnetite. The apparatus uses a minimum number of parts, which are of simple construction. The heat economy is good, since outgoing products are at relatively low temperature.

While I have shown and described certain preferred embodiments of my invention, it is apparent that other modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A method of converting hematite to magnetite comprising drying and preheating hematite ore fines in a first kiln, continuously transferring the fines from said first kiln to a second kiln, continuously introducing fresh reducing gas at an elevated temperature from an outside source to said second kiln and thereby reducing hematite in the fines to magnetite, continuously transferring the reduced fines from said second kiln to a third kiln, continuously passing gas which has gone through said s econd kiln and is at least mildly reducing through said third kiln, said last-named gas serving as a cooling medium for the fines and preventing reoxidation of the magnetite, continuously recycling gas from said third kiln through one of the other kilns, continuously passing gas which has gone through at least one other kiln through said first kiln, and burning in last-named gas in said first kiln to supply heat thereto.

2. A method as defined in claim 1 including a further step of recovering dust from gases which have passed through said kilns.

u 3. A method of converting hematite to magnetite com.

prising drying and preheating hematite ore fines in a first kiln, continuously transferring the fines from said first kiln to a second kiln, continuously introducing fresh reducing gas at an elevated temperature from an outside source to said second kiln and thereby reducing hematite in the fines to magnetite, continuously transferring the reduced fines from said second kiln 'to a third kiln, continuously passing gas which is at least mildly reducing through said third kiln, said last-named gas serving as a cooling medium for the fines and preventing reoxidation of the magnetite, continuously recycling gas from said third kiln through one of the other kilns, continuously passing gas from said second and third kilns through said first kiln, burning the last-named gas in said first kiln to supply heat thereto, and utilizing .gas from said rst kiln as the mildly reducing gas in said third kiln.

4. A method as defined in claim 3 including further steps of recovering dust from the gases leaving said first kiln and reducing hematite in this dust to magnetite.

5. A method as defined in claim y4 in which the recovered dust is reduced in said second kiln along With the ore fines.

6. A method as defined in claim 4 in which the recovered dust is reduced in a separate fiuidized bed reactor.

7. A method as defined in claim 3 in which said firstnamed reducing gas is generated by burning fuel with sufficient air only for partial combustion and enters said second kiln at a temperature of about 1800 to 2400 F.

8. A method as defined in claim 3 in which gases pass through said first and third kilns in a direction counter to the ore and through said second kiln in the same direction as the ore.

9. A method of converting hematite to magnetite comprising drying hematite ore fines and preheating them to a moderate temperature in a first kiln, continuously transferring the fines from said first kiln to a second kiln, continuously introducing fresh reducing gas at an elevated temperature from an outside source to said second kiln and thereby reducing hematite in the fines to magnetite, continuously transferring the reduced fines from said second kiln to a third kiln, continuously passing a portion of the gas from said second kiln through said third kiln, said last-named gas serving as a cooling medium for the fines and preventing reoxidation of the magnetite, continuously returning the gas from said third kiln to said second kiln, continuously passing another portion of the gas from said second kiln through said first kiln, and burning the last-named gas in said first kiln to supply heat thereto.

L10. A method as defined in claim 9 including further steps of recovering dust from gas leaving said first kiln and introducing this dust to said second kiln to reduce hematite therein to magnetite.

11. A method as defined in claim 9 in which the gas passes through each of said kilns in a direction counter to the ore and in which the gas introduced to said second kiln is at a temperature of 1500 to 1600 F.

12. An apparatus for converting hematite to magnetite comprising first, second and third kilns, means for passing hematite ore fines continuously through said kilns in succession, an outside source connected to said second kiln for continuously introducing a reducing ygas thereto at an elevated temperature to reduce hematite in the fines to magnetite, means for continuously passing gas which has gone through said second kiln and is at least mildly reducing through `said third kiln, said last-named .gas serving as a cooling medium for the fines and preventing reoxidation of the magnetite, means for passing gas which has gone through at least one other kiln through said first kiln, and means connected to said first kiln for burning the last-named gas therein to supply heat to said first kiln for drying and preheating the ore fines.

13. An apparatus as defined in claim 12 including means for recovering dust from gases which have passed through said kilns.

14. An apparatus as defined in claim 12 in which the gas which passes through said third kiln comes from said tfirst kiln, and the gas which passes through said first kiln comes from both said second and third kilns.

15. An apparatus as defined in claim 12 in which a portion of the gas from said second kiln passes through said third kiln and returns to said second kiln, and another portion of the gas from said second kiln passes through said first kiln.

(References on foilowing page) References Cited bythe Examiner UNITED STATES PATENTS 3,160,498 12/1964 Olt et al. 75-35 3,160,499 12/ 1964 Pfeiffer et a1. 75-35 Bradley 75-35 FOREIGN PATENTS Wechter 75-1 5 674,804 11/1963 Canada.

Shipley 75-1 Erck et al. 7)- 1 BENJAMIN HENKIN, Primaly Examiner. 

1. A METHOD OF CONVERTING HEMATITE TO MAGNETITE COPRISING DRYING AND PREHEATING HEMAITE ORE FINES IN A FIRST KILN, CONTINUJOUSLY TRANFERRING THE FINES FROM SAID FIRST KILN TO A SECOND KILN, CONTINUOUSLY INTRODUCING FRESH REDUCING GAS AT AN ELEVATED TEMPERATURE FROM AN OUTSIDE SOURCE TO SAID SECOND KILN AND THEREBY REDUCING HEMATITE IN THE FINES TO MAGNETITE, CONTINUOUSLY TRANSFERRING THE REDUCED FINES FROM SAID SECOND KILN TO A THIRD KILN, CONINUOUSLY PASSING GAS WHICH HAS GONE THROUGH SAID SECOND KILN AND IS AT LEAST MILDLY REDUCING THROUGH SAID THIRD KILN, SAID LAST-NAMED GAS SERVING AS A COOLING MEDIUM FOR THE FINES AND PREVENTING REOXIDATION OF THE MAGNETITE, CONTINUOUSLY RECYCLING GAS FROM SAID THIRD KILN THROUGH ONE OF THE OTHER KILNS, CONTINUOUSLY PASSING GAS WHICH HAS GONE THROUGH AT LEAST ONE OTHER KILN THROUGH SAID FIRST KILN, AND BURNING IN LAST-/NAMED GAS IN SAID FIRST KILN TO SUPPLY HEAT THERETO. 